1. Field of the Invention
The present invention relates to a fuel injection device of an engine for a vehicle.
2. Description of the Related Art
In an internal combustion engine constructed so that a required amount of fuel injection is determined by an amount of a depression of an accelerator pedal and an engine speed, and an amount of fuel corresponding to the required amount of fuel is injected, a problem arises in that a vehicle surges forward and backward when an output of the engine is quickly raised or reduced by an acceleration or deceleration operation. The reasons for this surging of the vehicle forward and backward are given as follows.
FIG. 22 shows a typical drive system of a vehicle, wherein A represents an engine B is an engine output shaft and C is a power transmitting system connected between the engine output shaft B and drive wheel D. The power transmitting system C includes a clutch, a transmission, and a propeller shaft or the like. Note, these elements are collectively and generally shown as one rod. In the thus-represented vehicle, a torsion is generated in the power transmitting system C during a drive of the vehicle, and the relative torsional angle generated between the opposed ends of the power transmitting system C at this time is hereinafter called a relative angle of torsion. This relative angle of torsion is represented by .theta. in FIG. 22. When the required fuel injection amount is constant and does not change, and the vehicle is in a cruising state, the relative angle of torsion .theta. is maintained at a fixed angle of torsion corresponding to the required fuel injection amount i.e., the output of the engine. The fixed angle of torsion corresponding to the required fuel injection amount is hereinafter called a converging angle of torsion, and this converging angle of torsion is represented by .theta.a and .theta.b in FIG. 23. Namely, when the required fuel injection amount is maintained at a constant value Qa in FIG. 23 and does not change, while the vehicle is in a cruising state, the relative angle of torsion .theta. is maintained at a constant converging angle of torsion .theta.a. Also, when the required fuel injection amount is maintained at a constant value Qb and does not change, while the vehicle is in the cruising state, the relative angle of torsion .theta. is maintained at a constant converging angle of torsion .theta.b. Accordingly, when the vehicle is in a cruising state, the relative angle of torsion .theta. is maintained at the constant converging angle of torsion corresponding to the required fuel injection amount.
When the vehicle is in a transient state wherein the required fuel injection amount is abruptly changed, however, the relative angle of torsion .theta. is not maintained at the converging angle of torsion corresponding to the required fuel injection amount. Namely, as shown in FIG. 23, when a driver quickly depresses the accelerator pedal and the required fuel injection amount is abruptly changed from Qa to Qb, the output of the engine is quickly raised, although the speed of the vehicle cannot be increased immediately after the raising of the output of the engine because the vehicle has a large mass. Accordingly, the relative angle of torsion .theta. at this time becomes larger than the converging angle of torsion .theta.b corresponding to the required fuel injection amount Qb, and a part of the increase in the output of the engine is stored in the power transmitting system C as elastic energy. Then, as shown in FIG. 23, the speed of the vehicle increases and the vehicle acceleration G increases. Since, at that time, torque due to the elastic energy stored in the power transmitting system C in addition to the output torque of the engine is imposed on the drive wheel D, the vehicle acceleration G becomes higher than an acceleration Gb determined by the output of the engine. When the vehicle acceleration G is higher than the acceleration Gb determined by the output of the engine, however, the relative angle of torsion .theta. of the power transmitting system C becomes inappropriate, the vehicle acceleration G is poor, i.e., the relative angle of torsion .theta. becomes smaller than the converging angle of torsion Qb corresponding to the required fuel injection amount Qb, and thus the vehicle acceleration G becomes lower than the acceleration Gb determined by the output of the engine. Therefore, when the required fuel injection amount Q is rapidly increased, the relative angle of torsion .theta. of the power transmitting system C is rapidly varied, and accordingly, the vehicle acceleration G is adversely affected, and thus the vehicle surges forward and backward. Since a vibration damping system is provided in the power transmitting system C, the amplitude of the relative angle of torsion .theta. in the power transmitting system C and the amplitude of the vehicle acceleration G is gradually lessened whereby the surging of the vehicle is gradually reduced, and when the speed of the vehicle increases after the acceleration is started, the vehicle acceleration Gb is gradually reduced. Nevertheless, as long as the required fuel injection amount Q is constant, even if the speed of the vehicle increases, the vehicle driving force is maintained at a constant value, so that as long as the required fuel injection amount Q is Qb, the relative angle of torsion .theta. is maintained at .theta.b. As understood from FIG. 23, such a forward and backward surging of the vehicle is also generated when the required fuel injection amount Q is lowered from Qb to Qa.
In a well-known internal combustion engine, the required fuel injection amount Q is gradually increased at a predetermined low speed, to thus reduce the forward and backward surging of the vehicle as shown by broken lines in FIG. 23, when a driver quickly depresses the accelerator pedal, and the required fuel injection amount Q is slowly reduced at low speed, as shown by the broken lines, when the amount of depression of the accelerator pedal is quickly changed (refer to Japanese Unexamined Patent Publication No. 60-19943).
When the required fuel injection amount Q is changed at a low speed under a transient operating state, however, the rise in the vehicle acceleration G is slow, as shown by broken lines in FIG. 23, and the response to an acceleration operation is poor. When the required fuel injection amount Q is slowly changed at a low speed, in such a transient operating state, the amplitude of the vehicle acceleration G becomes low, but the forward and backward surging of the vehicle is generated as usual.